1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to a method for selecting an electric power supply, a circuit and an apparatus thereof, and more particularly to a method for selecting an electric power supply by connecting or disconnecting switches and a display apparatus thereof.
2. Description of the Related Art
In a standby mode, which is a turn off status or not-in-use status when the apparatus is turned on, if the same amount of power is supplied as in-use status, power is wasted. So conventional apparatus uses a main power supply which supplies a high electric power and a sub power supply which supplies a low electric power like FIG. 1.
FIG. 1 illustrates a block diagram of a conventional apparatus 1 having electric power supplies. The conventional apparatus 1 includes a main power supply unit 10, a sub power supply unit 20, and a circuit unit 30 which includes a general circuit unit 31 and a control unit 32.
According to a tendency of integration, it is hard for the sub power supply unit 20 to supply an electric power only to the control unit 32. A part of general circuit unit 31 which is a set of circuits except the control unit 32 also is supplied with an electric power from the sub power supply unit 20 in the standby mode. It causes waste of an electric power.
In a general mode which is the in-use status, the sub power supply unit 20 also supplies an electric power to both the general circuit unit 31 and the control unit 32. It causes overload to the sub power supply unit 20.
A transformer which changes a voltage is used in many apparatus nowadays. The cost of the transformer is high and the size of the transformer is large. So it is desirable to use one transformer instead of two transformers.